Drainage element and method and machine for making same

ABSTRACT

The drainage element is made with a tubular membrane that encasing a mass of discrete aggregate. The membrane being gathered together at each end thereof, is water-permeable and has a plurality of interstices characterized in being of a size for the passage of water therethrough and the filtering of fine particles of solid material from the water passing through the membrane. A short length of pipe may be fabricated into one end only of the drainage element to provide for a hook-up to a sewage system or other system.

This invention relates to a drainage element and to a method and machine for making the same. More particularly, this invention relates to method and apparatus for making drainage elements having a light weight aggregate encased in a tubular membrane.

As is known, drainage elements have been constructed of loose aggregate, such as foam plastic elements, beads, and other lightweight materials with or without a perforated plastic pipe extending through and surrounded by the aggregate. Also, various techniques have been known for making such drainage elements in a manufacturing plant so that the individual drainage elements may then be shipped to a construction site for use. Examples of such techniques are described in U.S. Pat. Nos. 5,015,123; 5,154,543; 5,535,499; 5,657,527; and 6,173,483. Generally, these techniques use a process in which a supply of aggregate is fed under gravity into a horizontally disposed tubular mandrel through which a corrugated pipe is passed horizontally and on which a length of netting is mounted and fed off the mandrel as the aggregate fills the netting. In some embodiments, the aggregate is pneumatically conveyed into the netting while a reciprocating frame is provided for feeding the netting from a sleeve.

One of the drawbacks of this type of technique is that the length of the netting that is fed off the tubular mandrel is limited. Further, the apparatus, as described, requires a positive means for feeding the netting from the mandrel in order to prevent the netting from narrowing and becoming frictionally engaged with the outer surface of the mandrel.

Another drawback for this type of apparatus is that the apparatus requires an expenditure of energy to drive the loose fill material horizontally into the sleeve of netting.

Further, the drainage elements that are made in accordance with these techniques have been relatively flexible. As a result, drainage elements that are of long lengths, for example ten feet or more, run a risk of the netting catching on equipment in the field and becoming tom. In such cases, there is a risk that the aggregate within the netting may spill out. Where the netting is made of thin filaments so that the netting may be bunched up on the mandrel, there is also the risk of the filaments bursting to an extent that the aggregate can spill out of the drainage element. Also, the use of a netting allows the netting to catch on other elements during transport or during placement in a trench.

Further, use of a netting to contain the aggregate within the drainage elements while allowing water and/or effluent to pass through also allows fine particles of solid material to pass through into the aggregate from the surrounding environment. As a result, over time, the solid material can build up in the drainage element to such a degree that the drainage element becomes clogged and prevents a flow of water therethrough. In some cases, use has been made of covers in order to prevent top dirt fill from falling into the darinage elements. In other cases, such as described in U.S. Pat. No. 6,854,924, proposals have been made to incorporate a barrier material in a drainage element between the netting and the aggregate to prevent the passage of outside media, such as sand, dirt and soil, through the netting.

Accordingly, it is an object of the invention to provide a drainage element that is able to filter fine particles of solid material from entering into the drainage material.

It is another object of the invention to prevent clogging of drainage elements employing discrete aggregate when in use.

It is another object of the invention to avoid catching of a tubular drainage element on other elements during transport or being placed in a trench.

It is an object of this invention to provide an apparatus for making lightweight drainage elements on a substantially continuous basis.

It is another object of the invention to provide a method and apparatus of making drainage elements of compact construction in an inexpensive manner.

It is another object of the invention to provide a drainage element made with a tubular membrane that is tear-resistant.

It is another object of the invention to provide a drainage element that is relatively rigid.

It is another object of the invention to provide a simple means to prevent top dirt fill from falling between successive placed drainage elements in a trench.

It is an object of this invention of to provide a simple apparatus for making a drainage element of lightweight aggregate with a plastic pipe at one end only.

Briefly, the invention provides a drainage element comprising a mass of discrete aggregate defining passageways for a flow of fluid therethrough; a tubular membrane encasing the mass of discrete aggregate with the membrane being gathered together at each end thereof and tie means closing around each gathered end of the membrane to retain the aggregate therein.

In accordance with the invention, the membrane is water-permeable and has a plurality of interstices characterized in being of a size for the passage of water therethrough and the filtering of fine particles of solid material from the water passing through the membrane. In addition, the material has a high tear strength and does not run, for example in the manner of a nylon stocking. The membrane is made, for example, of spun bonded non-woven polyester.

A method of making the drainage element comprises the steps of forming a longitudinal strip of the membrane into a tubular cross-section with a pair of longitudinal edges disposed in overlapping relation to each other, securing the longitudinal edges together to define a tubular sleeve, closing one end of the sleeve, moving the sleeve along a linear path while filling the sleeve with aggregate and closing the opposite end of the sleeve about the pipe to form a drainage element.

In accordance with the invention, the overlapping edges of the membrane strip are adhesively secured to each other or are sewn together. For example, a longitudinal bead of adhesive, such as a heat sensitive glue, is placed between the longitudinal edges of the membrane and the edges are pressed together to bond the edges to each other.

In another embodiment, a pipe is moved coaxially into a rear of the sleeve while the sleeve is being filled with aggregate and the trailing end of the sleeve is secured to the pipe at an intermediate point of the pipe so that a length of the pipe projects from the rear end of the drainage element. In this embodiment, a screen is placed over the end of the pipe within the aggregate in order to prevent aggregate from entry into and out of the pipe. The resulting drainage element thus has a pipe at only one end that can be used to connect to a hook-up arrangement while the main body of the drainage element serves to convey water or an effluent therethrough. Also, the pipe may extend completely through the drainage element.

An apparatus for making the drainage element comprises a tube for passing a flow of aggregate therethrough, a forming collar for shaping a continuously supplied membrane strip into a sleeve about tube with the longitudinal edges thereof in overlapping relation to receive a flow of aggregate therein and a first means for securing the overlapped edges of the strip together. This means may adhesively secure the overlapped edges of the strip together by applying a bead of adhesive between the edges pressing the edges together using a roller.

The apparatus also includes a second means spaced from tube for intermittently applying tie means about the sleeve, a third means for moving a flow of aggregate through the tube for filling the sleeve with aggregate and a fourth means for moving the sleeve from the tube during filling of the sleeve with aggregate.

In making the drainage element of the second embodiment, the apparatus includes a drive means for intermittently moving a pipe coaxially through the tube into a rear of the sleeve while the sleeve is being filled with aggregate.

In each embodiment, the apparatus has a cutting means for cutting through the strip and pipe where inserted in order to form a single drainage element.

The aggregate that is employed in the drainage element may be a loose fill, plastic material or any other suitable aggregate.

As the membrane is being formed into a sleeve and placed over the tube, the membrane is gathered together at a point downstream of the tube and a tie means is applied to seal off one end of the sleeve. Aggregate is then passed through the tube and into the sleeve in a conventional manner. After a determined length of sleeve has been filled, the membrane is again gathered together and a tie means applied to seal off a second end of the sleeve. The cutting means is then operated to cut through the sleeve to form a drainage element. A series of interconnected drainage elements can thus be fabricated and shipped as such or the drainage elements may be separated from each other by severing the gathered together portions of the membrane at a mid-point for individual handling.

In the second embodiment of the apparatus, a pipe is fed coaxially into the tube from the rear and held in a fixed position. Thereafter, as above, the membrane is formed into a sleeve and placed over the tube. Then, the membrane is gathered together at a point downstream of the tube and a tie means is applied to seal off one end of the sleeve. Aggregate is then passed through the tube and into the sleeve moving around and past the pipe. After a determined length of sleeve has been filled, the pipe is fed forwardly a predetermined distance while the aggregate continues to fill the sleeve. The feeding of the pipe and aggregate then ceases, the rear end of the sleeve is gathered about the pipe and a tie means applied to secure the rear end of the sleeve to and about the pipe. The cutting means is then operated to cut through the trailing end of the sleeve and the pipe to for a drainage element.

In another embodiment, a plurality of strips of membrane may be supplied from different sources spaced peripherally about the tube, particularly where a large diameter drainage element is to be fabricated. In this embodiment, each strip is disposed peripherally about one part of the tube with the longitudinal edges overlapped with the adjacent strips. As above, the overlapped edges of the strips are secured together thereby forming multiple seams along the resulting sleeve.

The apparatus may be constructed so as to form the drainage elements along a vertical axis, for example in a manner as described in pending patent application Ser. No. 11/106,108 filed Apr. 14, 2005. Likewise, the apparatus may be mounted so that the drainage elements are formed on an angle to the horizontal. Also, the apparatus may be employed so as to form the drainage elements along a horizontal axis.

Where the apparatus is constructed to form a drainage elements along a vertical axis, the aggregate may be fed under gravity or may be fed pneumatically through the tube. Where the apparatus forms drainage elements along a horizontal axis, mechanical means or pneumatic means may be used to move the aggregate horizontally through the tube.

These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a side view of a drainage element in accordance with the invention;

FIG. 2 illustrates a partial side view of an apparatus for making the drainage element of FIG. 1 at start-up;

FIG. 3 illustrates a partial side view of the apparatus of FIG. 2 during an aggregate filling step in production;

FIG. 4 illustrates a partial side view of the apparatus of FIG. 2 during an insertion of a pipe in accordance with the invention;

FIG. 5 illustrates a partial side view of the apparatus of FIG. 2 during a final tieing step;

FIG. 6 illustrates a side view of a series of drainage elements laid in trench;

FIG. 7 illustrates a side view of an apparatus for making the drainage element of FIG. 1;

FIG. 8 illustrates a view of the apparatus of FIG. 7 rotated 90°;

FIG. 9 illustrates a schematic view of the apparatus of FIG. 7; and

FIG. 10 illustrates a perspective view of a cover placed over two abutting drainage elements in accordance with the invention.

Referring to FIG. 1, the drainage element 10 is comprised of a tubular membrane 11 and a mass of aggregate 12 within the tubular membrane 11. The aggregate 11 is made of discrete elements of a size to define passageways for a flow of fluid therethrough.

The tubular membrane 11 encases the mass of discrete aggregate 12 and is gathered together at each end with tie means 13, for example in the form of ties, closing around each gathered end of the membrane 11 to retain the aggregate therein.

In the illustrated embodiment, a pipe 14 extends from one end only of the drainage element 10. This pipe 14 extends into the aggregate 12 for a minor length of the drainage element 10. In addition, a screen 15 is placed over the internal end of the pipe for blocking entry of the aggregate 12 into the pipe 14 while allowing water to flow through.

The characteristics of the membrane 11 are such that the membrane is tear resistant. Hence, there is a reduced risk of netting being torn apart by catching on equipment in the field and spilling of the aggregate 12 out of the drainage element 10. Further, the membrane is water-permeable and has a plurality of interstices characterized in being of a size for the passage of water therethrough and the filtering of fine particles of solid material from the water passing through the membrane 11.

The membrane 11 is made of a spun bonded polyester material supplied by Oxco, Inc. of Charlotte, N.C. under model number PROWALL 70, A070F01WT1 for use in landscaping, specifically, as a weed retardant. Such a material is a non-woven material that has a grab tensile strength of 61/61 lbf (in each of two trasverse directions) and a grab elongation in % to break of 45/50 as measured under ASTM D-5034 and a tear strength of 23/23 lbf as measured under ASTM D-5733.

The membrane sleeve 11 is made of a material that is sufficiently flexible so that the ends of the sleeve 11 can be readily gathered together either about the pipe 14 or on itself to allow the tie means to be applied.

Of course, any other suitable material may be used for the membrane so long as the characteristics of strength, permeability,filtering and flexibility are provided.

The aggregate 12 is made of an expanded thermoplastic material and may be made of an expended thermoplastic material that has a residual capacity to expand upon further curing so that when fed into the membrane, a relatively rigid drainage element is obtained after curing, for example as a manner disclosed in copending patent application Ser. No. 11/248,753, filed Oct. 12, 2005.

Referring to FIGS. 7 and 8, the apparatus 16 for making a drainage element includes a delivery tube 17 disposed on a horizontal axis for passing a flow of aggregate (not shown) therethrough from top to bottom. The aggregate may be supplied in any suitable fashion, for example, the aggregate may be pneumatically conveyed into the tube 17 via a blower or the aggregate may be supplied through a vertical chute under gravity. The aggregate is preferably a loose-fill material, such as discrete elements of an expanded thermoplastic material.

In addition, the apparatus 16 includes a forming collar 18 disposed about the tube 17 for shaping a continuously supplied strip 19 of the membrane into a tubular shape about the tube 17 with the longitudinal edges 20,21 of the membrane 19 disposed in overlapping relation. The forming collar 18 is of any known suitable type such as that supplied by DSL Forming Collars of Houston, Tex.

During operation of the apparatus 16, the membrane strip 19 is supplied from a supply spool 22 on a continuous basis to the forming collar 18 so as to be shaped into a sleeve about the tube 17 in a known manner. The strip 19 is supplied in a width suitable to encompass the diameter of the tube 17 and to provide an overlap of the two edges 20, 21, for example of one or two inches or more.

The apparatus 16 also has a means of any suitable construction for securing the overlapped edges 20, 21 of the strip 19 together. In one embodiment, this means includes an applicator, such as a glue gun, 22′ (see FIG. 7) for applying a bead of adhesive between the overlapped edges 20,21 and a roller 23 for pressing the overlapped edges 20,21 together to ensure that the adhesive secures the overlapped edges 20,21 together. The adhesive may be a heat sensitive glue that cools quickly.

A Teflon® strip 24 is also applied to the tube 17 opposite the roller 23 to reduce wear on the tube 17 from the rotation of the roller 23 and to prevent the glue from sticking to the tube 17.

A cooling means may also be provided for cooling of the glue. Such a means may include a blower for blowing air onto the outside of the overlapped edges 20,21. Also, the tube 17 may be provided with holes where the overlapped edges 20,21 pass so that the air that is blown through the tube 17 may exit through the holes to cool the overlapped edges 20,21.This feature also provides an air cushion between the tube 17 and the sleeve 11 so as to prevent the sleeve 11 from sticking to the tube 17 while cooling the sleeve 11.

In another embodiment, a sewing, machine (not shown) may be used to sew the edges 20, 21 of the membrane strip 19 together. In this case, the edges 20, 21 would be disposed radially of the tube 17 and in parallel relation to each other.

The apparatus 16 is provided with a means in the form of a capstan arrangement 25 on diametrically opposite sides of the tube 17 in order to move the formed sleeve of membrane material along the tube 17. The capstan arrangement 25 is comprised of a pair of endless belt devices which are automatically operated in synchronism in order to move the sleeve 11 off the tube 17.

Referring to FIG. 9, wherein like reference characters indicate like parts as above, the apparatus 16 includes a hopper (not shown) for receiving loose fill elements, the elongated sleeve 11 that extends horizontally from the hopper, a means in the form of a blower 26 for blowing the loose fill elements from the hopper into the sleeve 11 and the capstan arrangement 25 near one end of the tube 17 for feeding the sleeve 11 off the tube 17.

The apparatus also employs a means 27 spaced from the tube 17 for intermittently applying the ties 13 to the gathered ends of the membrane 11 as well as a cutting means 28 for cutting through the gathered ends of the membrane 11 and any pipe 14 thereat.

In addition, a sleeve 29 is spaced from the tube 17 to receive the forward end of a drainage element (not shown) that is being fabricated. A sensor 30 is also disposed within the sleeve 29 at a pre-determined point for sensing the forward end of a drainage element being fabricated.

A means such as a perforated pipe feeder 31 is provided for delivering a continuous length of perforated pipe 14 within the tube 17. When this option is used, the loose fill elements surround the pipe in a circumferential manner within the tube 17.

The hopper (not shown) is of conventional structure to receive and deliver a flow of loose fill elements vertically, horizontally or on an incline.

The blower 26 is an off-the-shelf item, for example, a Quickdraft 20 HP with Venturi that receives the loose fill elements from the hopper and blows the elements into the elongated tube 17. The operation of the blower 26 is such that only approximately six to eight inches of the tube 17 at the exit end is filled with the loose fill elements. The air that is blown into the tube 17 escapes through the loose fill elements and the exit end of the tube 17 and through the sleeve 11.

The tube 17 is of circular shape with an outside diameter, for example of 10 inches and is initially loaded with the membrane sleeve 11 of a 10 inch diameter.

Referring to FIG. 2, wherein like reference characters indicate like parts as above, at start-up, the pipe feeder 31 (see FIG. 9) of the apparatus 16 is operated so that a length of pipe 14 is moved to the front of the tube 17. A screen 15 is then fitted over the end of the pipe 14. During this time, aggregate is not fed into the tube 17.

Thereafter, the forward end of the membrane 11 is gathered and a tie 13 applied to close this end of the membrane sleeve 11.

Next, referring to FIGS. 3 and 4, the blower 26 (see FIG. 9) is actuated to blow aggregate into the sleeve 11 and the capstan arrangement 25 is actuated to move the sleeve 11 from the tube 17 while the pipe remains fixed. The drainage element being formed then moves into the sleeve 29 (see FIG. 9) until reaching the sensor 30.

Referring to FIG. 5, when the sensor 30 detects the presence of the drainage element being formed, a signal is emitted to the pipe feeder 31 (see FIG. 9) to move the pipe 14 forwardly a predetermined distance, for example 6 to 10 inches or more while aggregate is still being fed into the sleeve. After a programmed time, the blower 26 is stopped to cease delivery of aggregate into the sleeve. However, the feeding of the sleeve 11 off the tube 17 continues for a short time sufficient to allow the rear end of the sleeve 11 to be tied about the pipe 14 without interference from the aggregate 12. Alternatively, the feeding of the sleeve 11 may be interrupted or not during this time.

After feeding of the aggregate ceases, the tying means 27 is actuated to gather the rear end of the membrane 11 about the pipe 14 and to apply a tie 13 to close the rear end of the membrane 11 onto the pipe 14. The cutting means 28 is then actuated to cut through the gathered end of the membrane 11 and the pipe 14 to form the drainage element 10 with the pipe 14 projecting from 1 to 6 inches from the end of the drainage element 10.

Thereafter, the exposed end of the pipe 14 within the tube 17 is fitted with a screen and the process repeated.

The apparatus 16 is operated so that the membrane strip 19 is continuously formed into a sleeve about the tube 17 and moved off the tube 17 via the conveyors 25 while aggregate is delivered on an intermittent basis through the tube 17 for passage into the formed sleeve outside the outlet of the tube 17. Any suitable valving may be used to interrupt the flow of aggregate into the tube 17 or from the tube 17 during which time the tying means 27 spaced from the tube 17 is operated to gather and secure the membrane 11 to form an end of a drainage unit and to contain the aggregate therein.

Referring to FIG. 6, the drainage element 10 with the pipe 14 extension may be aligned in a trench with a series of drainage elements 10′ made without a pipe. In this case, the pipe 14 of the drainage element 10 is connected to a source of effluent, such as in a sewage system or to any other hook-up arrangement. The effluent passing longitudinally through the drainage element 10 then passes longitudinally into the next drainage element and so on.

Where the drainage elements are employed in a drainage system, water is able to pass through the membrane sleeve 11 of each drainage element in a filtered manner to flow through the aggregate 12. The water may percolate downwardly to again pass through the sleeve into the ground or the water may flow longitudinally of the drainage elements to flow away from the source. In either case, clogging of the aggregate with soil is prevented.

Referring to FIG. 6, a cover 32 is placed in bridging relation over the ends of two abutting drainage elements 10,10′ in order to prevent soil and the like from dropping into the space between abutting drainage elements 10,10′. As shown in FIG. 10, each cover is preformed into a generally U-shape with sides 33 that extend downwardly about 12 inches and a central arched section that conforms to the periphery of a drainage element. Typically, a stack of these covers 32 would be supplied in the field so that each may be individually placed over a joint between two drainage elements. The length of each cover 32 is about 6 to 12 inches to ensure bridging over of any gaps between successive drainage elements. The use of the small length of the covers 32 is more economical than using elongated covers that cover the entire length of a drainage element.

The combination of the rigid drainage elements 10,10′ and the covers 32 form a worm hole for water to pass through.

The use of a drainage element with a stub pipe of limited length makes the drainage element less expensive to make and faster to manufacture.

The illustrated embodiment shows the tube 17 being disposed on a horizontal axis. However, the tube 17 may also be disposed at an angle to the vertical or may be disposed on a vertical axis.

The material of the membrane 11 is such that the diameter of the membrane remains constant throughout the operation of the apparatus 16. That is to say, there is no necking-down of the membrane during travel on or off the tube. Thus, the membrane is able to slide off the tube 17 without undue frictional grabbing of the tube 17. Further, the membrane may be formed of a diameter greater than the diameter of the tube 17 to allow the membrane to be loosely held on the tube 17.

The strength of the membrane 11 allows the aggregate to be fed under a high compaction force so that the resulting drainage element has a high degree of rigidity. Further, where the aggregate expands upon curing within the membrane, such as described in copending patent application Ser. No. 11/248,753, filed Oct. 12, 2005, the degree of rigidity is increased without tearing of the membrane.

The nature of the membrane 11 is such that the membrane may be printed. This may be of value in designating the use of a drainage element in the field. Further, the membrane may be embossed, for example, with hemisperical embossments 34 as shown in FIG. 1 of up to ⅛ inch in height to increase the surface area for water to pass through.

The drainage elements that are formed may be of any suitable diameter. In this respect, the tube 17 may be made of a diameter to suit the diametric size of the drainage element desired. Also, for very large diameter drainage elements, the strip 19 of membrane may be made of multiple lengths of membrane that are spliced together in parallel relation to provide a greater width of strip.

Where the cross-section of a drainage element is to be made other than circular, for example, of an oval or elliptical shape, the tube 17 may be made of a complementary shape and the forming collar may be made to form the strip 19 about such a tube.

The invention thus provides a drainage element that is able to filter fine particles of solid material from effluent entering into the element and that prevents clogging of the discrete aggregate when in use.

Further, the invention provides a drainage element that is provided with a tear resistant cover that reduces the risk that the drainage element may be tom open if snagged on equipment in the field.

Still further, the invention provides an economical method for making a drainage element with light weight aggregate that prevents soil and the like from passing into the aggregate. 

1. A drainage element comprising a mass of discrete aggregate defining passageways for a flow of fluid therethrough; a tubular membrane encasing said mass of discrete aggregate, said membrane being gathered together at each end thereof and being water-permeable and having a plurality of interstices characterized in being of a size for the passage of water therethrough and the filtering of fine particles of solid material from the water passing through said membrane; and tie means closing around each gathered end of said membrane to retain said aggregate therein.
 2. A drainage element as set forth in claim 1 wherein said membrane has a grab tensile strength of 61/61 lbf as measured under ASTM D-5034 and a grab elongation to break in % of 45/50 as measured under ASTM D-5034.
 3. A drainage element as set forth in claim 1 where said membrane is made of spun bonded non-woven polyester.
 4. A drainage element as set forth in claim 1 wherein said membrane has at least a pair of overlapped longitudinal edges adhesively secured to each other.
 5. A drainage element as set forth in claim 1 wherein said membrane has at least a pair of sewn together longitudinal edges.
 6. A drainage element as set forth in claim 1 further comprising a pipe extending from within said mass of aggregate and beyond one end of said tubular membrane, said pipe being of a length less than the length of said tubular membrane.
 7. A drainage element as set forth in claim 5 further comprising a screen disposed over an end of said pipe within said mass of aggregate for blocking entry of said aggregate into said pipe.
 8. A drainage element as set forth in claim 5 wherein said tie means at said one end of said tubular membrane is secured about said pipe.
 9. A drainage element as set forth in claim 1 further comprising a pipe extending from within said mass of aggregate and beyond each end of said tubular membrane.
 10. A drainage element as set forth in claim 1 wherein said membrane is embossed to increase the surface area thereof.
 11. A drainage element comprising a mass of discrete aggregate defining passageways for a flow of fluid therethrough; a tubular membrane encasing said mass of discrete aggregate; a pipe extending from within said mass of aggregate and beyond one end of said tubular membrane, said pipe being of a length less than the length of said tubular membrane. tie means closing around each end of said membrane to retain said aggregate therein.
 12. A drainage element as set forth in claim 10 further comprising a screen disposed over an end of said pipe within said mass of aggregate for blocking entry of said aggregate into said pipe.
 13. A drainage element as set forth in claim 10 wherein said tie means at said one end of said tubular membrane is secured about said pipe.
 14. A drainage element as set forth in claim 10 wherein said membrane is embossed to increase the surface area thereof.
 15. A method of making a drainage element comprising the steps of forming a longitudinal strip of a membrane into a tubular cross-section about a longitudinal axis thereof with a pair of longitudinal edges disposed in overlapping relation to each other, said membrane characterized in being of a size for the passage of water therethrough and the filtering of fine particles of solid material from the water passing through said membrane; securing said longitudinal edges together to define a tubular sleeve; closing one end of the sleeve; moving said sleeve along a linear path while filling said sleeve with aggregate; moving a pipe coaxially into a rear of said sleeve while continuing to fill said sleeve with aggregate; and closing the opposite end of said sleeve about the pipe to form a drainage element.
 16. A method as set forth in claim 15 further comprising the step of placing a longitudinal bead of adhesive between said longitudinal edges of said membrane and pressing said edges together to bond said edges to each other.
 17. A method as set forth in claim 15 further comprising the step of placing a screen over an open end of said pipe prior to said step of closing one end of said sleeve.
 18. An apparatus for making a drainage element comprising a tube for passing a flow of aggregate therethrough; a forming collar for shaping a continuously supplied membrane strip having a pair of longitudinal edges into a sleeve about said tube with the longitudinal edges thereof in overlapping relation to receive a flow of aggregate therein; first means for securing the overlapped edges of the strip together; second means spaced from said tube for intermittently applying tie means about the sleeve; third means for moving a flow of aggregate through said tube for filling the sleeve with aggregate; fourth means for moving the sleeve from said tube during filling of the sleeve with aggregate; and drive means for intermittently moving a pipe coaxially through said tube into a rear of the sleeve while filling the sleeve with aggregate.
 19. An apparatus as set forth in claim 18 wherein said first means adhesively secures the overlapped edges of the strip together.
 20. An apparatus as set forth in claim 19 wherein said first means includes at least one roller for pressing the overlapped edges of the strip together.
 21. An apparatus as set forth in claim 18 further comprising a cutting means for cutting through the strip and pipe. 